Enter a room's length, width and height, choose whether you are boarding the ceiling, and get the drywall sheets, screws, joint compound and tape to board and finish it.
Openings (deducted from walls)
Boarded area
45.6 sq ft
Screws
~64
Joint compound
~6 lb · 475 ft²/box
Joint tape
~17 ft
Drywall (plasterboard) is sold in sheets that clad the studs, then the joints between them are taped and filled. The calculator sizes both the boarding and the finishing from your room dimensions:
wall area = 2 × (length + width) × height - openings
ceiling = length × width (if you board it)
sheets = ceil( (wall area + ceiling) × wastage ÷ sheet area )
screws = sheets × 32
compound = boarded area × 0.64 kg/m²
tape = boarded area × 1.2 m/m²
By default the wall area treats the room as a closed box. Add the doors and windows on each room and the calculator subtracts their area from the walls - handy when a room has large openings that would otherwise have you buying boards you only cut to waste. Leave the openings off for a quick closed-box estimate where the wastage allowance covers the offcuts.
This example follows the unit system you pick in the calculator above.
A 12 × 10 ft room, 8 ft high, ceiling boarded, with 8 × 4 ft sheets and 10% wastage:
| Item | Rule of thumb |
|---|---|
| Screws | ~32 per sheet (200-300 mm spacing); ceilings need more |
| Joint compound | ~0.6 kg/m² for a taped three-coat finish |
| Joint tape | ~1.2 m/m² of board |
| Corner bead | The length of each external corner, bought separately |
Work out the area to board - the walls are the room perimeter times the ceiling height, plus the ceiling itself if you are boarding it - then divide by the area of one sheet and add wastage. A 4 × 3 m room 2.4 m high with the ceiling boarded comes to 45.6 m²; with 2.4 × 1.2 m sheets and 10% wastage that is 18 sheets. Enter your room and sheet size above for the exact figure.
Allow roughly 0.6 kg of joint compound per square metre of board for a taped, three-coat finish - about a 4.5 gallon (61.7 lb) box per 44 m² (475 sq ft). For tape, allow about 1.2 m per square metre (370 linear feet per 1,000 sq ft). The calculator works both out from your boarded area.
Around 32 screws fix a standard 8 × 4 ft (2.4 × 1.2 m) sheet to studs at 16 inch (400 mm) centres - roughly a screw every 200-300 mm around the edges and down the centre studs. Ceilings are fixed more densely. The calculator multiplies your sheet count by 32 as a buy estimate.
If you are drywalling a ceiling as well as the walls, tick "Board the ceiling" on each room and the calculator adds the floor area (length × width) to the boarded total. Board the ceiling first so the wall sheets tuck up under it and support the edges. Leave it unticked for a walls-only job.
Add each door and window to the room and the calculator deducts its area from the walls before working out the sheets. Use the "+ Door" and "+ Window" buttons for a standard size, then edit the width, height and quantity to match. For a small room with one or two openings you can skip this and let the wastage allowance cover the offcuts; deduct them when the openings are large enough to save a sheet or two.
Add 10% for a simple room and 15% where there are lots of doors, windows, alcoves or services to cut around. Offcuts from openings can often be reused lower down or above doors, but it is safer to round up than to be one sheet short and stop the job.
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